A working Sprectrum Analyzer schematic????

Discussion in 'The Projects Forum' started by dyeraaron, Nov 23, 2009.

  1. dyeraaron

    Thread Starter Active Member

    Oct 27, 2008
    57
    0
    Hey guys,

    I'm going into my final 2 classes for my degree @ ITT in electronic Engineering. I wanted to build two things for my capstone...a Thermostat and then an LED or Bar Graph LED spectrum Analyzer...Now I've seen all the You tube videos where people post there analyzer up and they look great...problem is I can't ever see any schematics.....I'm just trying to find something with an LM3915 and a few 741 op Amps for my filters and maybe a 4 x 10 or 5 x 10 rows of LEDS. Please help...any input is deeply appreciated.
     
  2. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    here you go.....[​IMG]
     
  3. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    Have you actually built that circuit? Doesn't look right to me for a spectrum analyzer. Where are the filters?
     
  4. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234

    Filters for what?? The LM3916 does all the filtering/decoding of one signal...... And yes I have built it before, and it works quite nicely.....
     
    Last edited: Nov 24, 2009
  5. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    How does it filter the different notch frequencies? It's only a simple level converter.

    What frequency do each of the LED columns represent?
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
  7. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    here is a link to a kit for such a device based on the LM3916 Audio VU Meter IC.... reasonably priced I might say...... >> http://www.vakits.com/index.php?cPath=169

    I might acquire some for x-mas presents for some of my employees, so they can practice some soldering skills and circuit assembly (These guys can spin a wrench just as good as anybody, but have them solder an LED to a PCB, and you might be in for a surprise!!).......

    My .02
     
  8. rogs

    Active Member

    Aug 28, 2009
    279
    37
    That was my reaction too! I seemed to remember that there was more to a spectrum analyser than a VU meter driver. Band pass filters for a start!

    This schematic of an old Velleman kit:
    http://www.animeguru.com/images/velleman/k4300.html
    gives more of an idea. Sadly the A/D is obsolete, so it's not available any more.

    Shows the necessary building blocks though.
     
    Last edited: Nov 23, 2009
  9. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234
    ok, If you have Eagle Cad, here is a link to the projects download section (http://www.cadsoftusa.com/cgi-bin/d.../download.htm.en&dir=eagle/userfiles/projects), look for "audio_spectrum_analyzer.zip", and there is a complete project including all the filters....

    On a side note, the OP should be the one asking these questions, I was kind of expecting him to ask that question, and I would have gone on from there and told him about filtering for each frequency notch he wants.... I did not want to do "all the work" for him as we have always suggested the OP should do most of the work and we are here to guide them along the way..... so lets let the op do the asking, then we could direct more of the attention to guiding him as he does his school work....

    My .02
     
    Last edited: Nov 23, 2009
  10. dyeraaron

    Thread Starter Active Member

    Oct 27, 2008
    57
    0
    Morse,

    Thanks for the help to begin with.....The last project you had posted...the audio_spectrum_analyzer.zip...I had found this before....I built the 100 LED matrix for my display last night and its looking good so far......I have both LM3915 and LM3914 but I'm going to go with the LM3914. Do you guys have any suggestions on Op amps to use...I have 741s, 386s an LM3900 dual Op amp and LM224 Dual Op amp. I didn't know about the LM3916 though...thats cool.... This may sound like a dumb question..but for the entire circuits input...Would this come from a channel on the stereo where you plug your speakers in...???? I was thinking more like an RCA jack but where could I plug the other male side into?
     
  11. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    I don't see it either. Asking question is always allowed by forum rules as I understand them. It keeps us honest (and I include myself in that statement).

    I see the scan, I see the bargraph, but I don't see the frequency discrimination? I'm not trying to give hard time, just trying to learn something new.
     
  12. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234

    This was just a starting point for him to add filters to discriminate the different frequencies......
     
  13. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
    1,758
    98
    I can't figure out what your original circuits function is?
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The 741 is 42 years old and has a max output at 9kHz.
    The LM386 is a power amplifier, not an opamp. It has built-in negative feedback.
    The obsolete LM3900 had four very odd opamps.
    The LM224 quad opamp has a max output at about 2kHz.

    Use TL071 single, TL072 dual or TL074 quad low noise wide bandwidth inexpensive audio opamps.
     
  15. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234

    go here, look at the kit and ask them why they call this kit and ask them why they say it is an "Audio Spectrum Analyzer" http://www.vakits.com/index.php?cPath=169

    when I built this particular circuit, I had 7 circuits connected to a 7 band equalizer (Thus turning it into a 7 Band GRAPHIC equalizer), so the input was coming off of each band..... so the input DOES need filtering for the different frequencies.....

    My .02
     
  16. dyeraaron

    Thread Starter Active Member

    Oct 27, 2008
    57
    0
    Thanks for the help guys.....Like I said...my matrix is complete and I'm going to start on my bandpass filters soon (10 of them) I'm thinking of using what a schematic I have says to use in the TL084 op amp.... one last thing....the input signal going to the bandpass circuitry....does this come from a output channel port of a stereo or tv...etc. ???????
     
  17. BMorse

    Senior Member

    Sep 26, 2009
    2,675
    234

    That would connect to the line out or speaker level connections......
     
  18. dyeraaron

    Thread Starter Active Member

    Oct 27, 2008
    57
    0
    Thanks again
     
Loading...